1. Field of the Invention
The invention relates to a chain, more particularly to a chain having a link unit for connecting two ends of a chain body.
2. Description of the Related Art
Taiwanese Patent Publication No. 171756 discloses a conventional chain. Referring to FIGS. 1 and 2, the conventional chain 1 comprises a chain body 11 and a link unit 10 for connecting two ends of the chain body 11. The chain body 11 includes a pair of connecting units 111 and a plurality of outer and inner chain plates 113, 114 connected to the connecting units 111. Each of the connecting units 111 has a pair of connecting chain plates 112 spaced apart from each other in a first direction (L). The link unit 10 includes a pair of link plates 12 spaced apart from each other in the first direction (L), and a pair of link pins 13. Each of the link plates 12 extends in a second direction (L1) transverse to the first direction (L), and has a pair of end plate parts 121 and a connecting plate part 122 interconnecting the end plate parts 121. One of the end plate parts 121 is formed with a mounting hole 123, and the other one of the end plate parts 121 is formed with a gourd-shaped retaining hole 124. The connecting plate part 122 has a pair of connecting surfaces 120 that extends in the second direction (L1). The retaining hole 124 has an insert hole portion 125 proximate to the connecting plate part 122, a retaining hole portion 126 distal from the connecting plate part 122, and a neck hole portion 127 disposed between the insert hole portion 125 and retaining hole portion 126. The insert hole portion 125 has a diameter larger than that of the retaining hole portion 126. Each of the link pins 13 has a mounting end portion 131 disposed in the mounting hole 123 in one of the link plates 12, and an engaging end portion 132 engaging the retaining hole portion 126 of the retaining hole 124 in the other one of the link plates 12. During assembling, each of the link pins 13 is inserted into the insert hole portion 125 of the corresponding retaining hole 124, and is then moved into the retaining hole portion 126 of the corresponding retaining hole 124.
However, when the conventional chain 1 is in use, the connecting units 111 may be pushed to move toward each other. If this occurs, the engaging end portion 132 of each of the link pins 13 may move from the corresponding retaining hole portion 126 into the corresponding insert hole portion 125, thereby resulting in separation of the link plates 12 from the connecting units 111. Moreover, the connecting surfaces 120 of the connecting plate part 122 of each of the link plates 12 have to be configured to be parallel to each other so as to meet the structural strength requirement of the link plates 12. Therefore, the outlines of the link plates 12 are different from those of the outer chain plates 113. If the conventional chain 1 is adapted for use in a multi-speed bicycle, the outline difference between the link plates 12 and the outer chain plates 113 will obstruct the smooth speed-changing operation of the conventional chain 1.